The present invention relates to isolating trenches and methods of producing such trenches.
In order to isolate components in integrated circuits from each other refilled trench structures have been developed. There are many different ways of forming such trenches which can be etched through a silicon layer into an underlying buried insulating oxide layer or through a silicon substrate into an underlying silicon layer which has the opposite type of doping in relation to the layer which is to be laterally insulated. Methods of making such trenches are shown in Wolf, S., "Silicon Processing for the VLSI Era Volume II", pages 45-56, ISBN-0-961672-4-5, 1990, Lattice Press USA.
A problem with the use of trenches for isolating components is that the small width of the trenches make them vulnerable to foreign particles or defects in the material, both of which can short circuit the desired electrical insulation. This is particularly difficult to cure in the case of components having long total trench lengths. Another problem with trench structures is that the different thermal properties of the materials in and surrounding the trenches can lead to mechanical stresses occurring in the trench material or the surrounding silicon. A further problem with trench structures is that steps are often formed over trenches during their manufacture. These steps can trap conductive material in undesirable regions during subsequent processing and can cause short circuits. An example of such undesirable conductive material is polysilicon strings which remain in the trench edges and can go all the way around a component. These strings can then cause short circuits between two conductors which cross the trench and are in contact with the strings.